Levitation and heating of electrically conductive materials by means of electromagnetic resonators



Aug- 7, 1956 E. c. oKREss 2,758,188

LEVITATION AND HEATING OF ELECTRICALLY CONDUCTIVE MATERIALS BY MEANS OF ELECTROMAGNETIC RESONATORS Filed Aug. 27, 1953 2 Sheets-Sheet 1 LEVITATION AND HEATING 0F ELECTEICALLY coNDUcTIvE MATERIALS BY MEANS oF ELECTROMAGNETIC REsoNAToRs Filed Aug. 27, 195:5

2 8 t 8 A e l m o0 S 5 qw 7 .t e e h S 2 E. C. OKRESS Aug. 7, 1956 a. 5 1 @n n J T N mm ,W A m M a Y M n B.

l Y FI United States Patent() LEVITATION AND HEATING OF ELECTRICALLY CONDUCTIVE MATERIALS BY MEANS OF ELECTROMAGNETC RESONATORS Ernest C. Okress, Montclair, N. J., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application August Z7, 1953, Serial No. 376,816

3 Claims. (Cl. 219--10.55)

This invention relates to heating and/or melting of electrically Conductive materials in any form or shape, while levitated by properly distributed alternating magnetic fields in air, vacuum or inert gas, without a conning container or Crucible.

The principal object of my invention, generally considered, is to provide a method and apparatus for heating conductive materials, comprising a hollow body formed of conductive material and made a resonator by supplying thereto electromagnetic energy at a predetermined frequency, whereby a conductive object disposed in its interior may be levitated by the electromagnetic fields produced therein, and means for moving such an object finto the body 'enclosing said fields, whereby it may be levitated and heated to the desired extent, out of Contact with a Crucible or other container, potentially-contaminating at the elevated temperature involved.

Another object of my invention is to produce an electromagnetic eld, inside of a hollow body and so distributed that metal or other conductive material to be melted therein does not touch any enclosure, and while so levitating the material, if desired, melting it by power derived from said field.

A further object of my invention is to produce a hollow, desirably spherical, resonator, means for introducing an inert atmosphere thereinto, and means for supplying suitable electromagnetic power thereto as by means of a coaxial'line or wave guide, in order to effect by means of electromagnetic induction, a desired heating action on an object suspended in its interior.

Other objects and advantages will become apparent as the description proceeds.

Referring to the drawings:

Fig. 1 is a vertical mid-sectional view of apparatus for producing an electromagnetic field confined in a hollow object, whereby said field may occur in air, in a vacuum, or in an inert atmosphere, for enclosing conductive material to be levitated and/ or heated, together with means for raising to and supporting such material in a position near the center of the hollow body, so that the eld produced will exert the desired levitation, and then withdrawing said supporting means.

Fig. 2 is a fragmentary vertical sectional view on the line H II of Fig. l, in the direction of the arrows.

Fig. 3 is a fragmentary vertical sectional View corresponding to that of Fig. l, bu't showing that portion of the apparatus above the line A-A of Fig. l, that is showing that part of the coaxial line therebeyond for connection with the source of electromagnetic energy and an exhaust system.

Fig. 4 is a fragmentary vertical mid-sectional view of a portion of the apparatus illustrated in Fig. l, but showing it in position where the enclosed conductive material has been melted and is being withdrawn from the resonator in liquid form and caught iin Va receptacle thereben'eath.

Fig. 5 is a diagrammatic vertical mid-sectional view illustrating a mode of electromagnetic eld which may be generated in the concentric spherical resonator.

Figs. 6 and 7 are views, corresponding to Fig. 5, but showing other forms of desirable fields which may be generated inside the disclosed concentric spherical resonator. Other shapes of resonators may be used, e. g. ellipsoidal, pear shaped, conical, cubical, etc.

Fig. 8 is a fragmentary vertical sectional view showing an alternative means of coupling the resonator to a generator of high frequency power.

In melting conductive materials such as metals, particularly in melting the more reactive high-melting-point metals, such as titanium, zirconium, vanadium, tantalum, molybdenum and other metals of similar chemical and physical characteristics, difculty has been encountered in the selection of Crucible material. When such metals are melted, they react with the material of the Crucible to some extent, or other reactions occur which adversely affect the quality of the melt.

In order to overcome such difficulties, there has been devised a novel method and apparatus wherein such metal or other conductive material may be heated and melted while out of Contact with any confining material with which it might react, whereby no refractory crucibles are necessary to hold the metal for melting. Such a method and apparatus is described and claimed in Patent No. 2,686,864, dated Aug. 17, 1954, which was granted to D. M. Wroughton and the present applicant `and is owned by the assignee of the present application. See also I. of Appl. Phys., May 1952, December 1952.

ln accordance with said patent, the conductive material is levitated in air, a vacuum, or an inert atmosphere, confined by a suitable vessel or bell jar, of material such as a quartz, or 96% silica glass such Vas manufactured by the Corning Glass Works under the name Vycon by means of an alternating magnetic field or fields, so distributed between, for example, two coaxial coils, that the material to lbe melted does not touch any solid matter, and while so levitating, melting it by alternating electrical energy from the surrounding coil system.

The present invention concerns an improvement over that of the patent referred to. It involves the employment of a resonator excited by electromagnetic fields from a suitable oscillator. A preferred form of the resonator involves a hollow spherical object, formed as a relatively-thin film of highly-conductive material, such as silver, on a copper base, desirably polished on its interior surfaces, and provided with cooling means lying adjacent thereto. Means are provided for placing a couductive object or charge to be levitated and heated near the center of this resonator and then withdrawing the placing means, after electromagnetic energy has been applied to levitate the object near the center of said resonator.

The placing means is desirably formed of nonconductive material, such as fused quartz, and after positioning the object, it may then bereplaced by a metal rod closing the aperture through which the placing means passed, so as to malte the resonator electrically continuous and thereby avoid local weakness in the field produced therein. Such -a system has some striking advantages, las Compared vwith that described in the Wroughton and Okress patent, above referred to, although there are some disadvantages, which however only set a lower limit to the frequency which can be used practically in order to :avoid unduly increasing the size of the apparatus.

Some of the striking advantages of the proposed invention are:

l. By virtue of the possibility by making highly reliecting the interior surface of the shell or resonator body, :there is encountered only negligible thermal radiation loss from the levitated charge.

2. The resonator almost completely confines the electromagnetic eld, so that negligible eld loss occurs. The word almost is here used in order to allow for radiation losses due to observation holes. Some unavoidable power loss occurs in the walls of the resonator and coaxial line or waveguide feed, due to the fact that the high-frequency resistances of the materials used are not zero.

3. A more desirable eld distribution can be effected than that which can be realized with open coils, and certain undesirable field sinks are practically eliminated.

4. The envelope of the resonator may serve as a vacuum chamber or one containing inert or reducing gas.

5. The electromagnetic power to the resonator can be efficiently and conveniently supplied, as by means of a coaxial line or waveguide.

None of the foregoing advantages are possessed by the invention of the patent above referred to.

The proper mode of oscillation may be determined from the conditions for sustenance of the E and H waves, as will be understood by those skilled in the art.

ln a concentric sperical resonator, as a preferred example, the allowed fields comprise the TH modes (H. M. MacDonald, Electric Waves, Cambridge, 1902, p. 53):

(l) and the TE modes (MacDonald reference above, p. 52): Jn+5(kr0)J-n1(k1'1)=Jn+1(kr1)J-n4(kf0) (2) where denotes partial l denotes the Bessel function of order indicated by subscript; order n=0, 1, 2, k denotes the numeric w/v v denotes velocity of propagation of the field in the conned medium=c/\/en c denotes Velocity of light in free space e denotes dielectric constant of medium n denotes permeability of medium w denotes the angular frequency, 21W v denotes the frequency ro denotes radius of inner sphere (ideal case); and r1 denotes the inside radius of outer sphere The Equations 1 and 2 define the relationship between the frequencies of the electromagnetic field modes, TH and TE, respectively, and the geometry of the concentric spherical resonator.

Prom these modes can be selected the desired eld as defined in the above-mentioned patent.

To determine the modes and hence character of the associated fields requires an evaluation of the roots of the two foregoing relations. No systematic solutions of l have appeared in the literature except for the limited case of 17:1, for which the solution (l. I. Thomson, Recent Researches in Electricity and Magnetism, Clarendon, 1893, chapter IV, article 315) is:

4 Although the solution of (2) for n=1 is:

G(7`1-10) tan 76(71 T0) 1+k2r0r1 solutions or roots for other orders are given by Jahnke- Ernde (E. Jahnke and F. Emde, Tables of Functions, Teubner, 1938, pp. 204-206) in which (2) is expressed as and this can be placed in the form (2) by making the following substitutions (lahnke-Emde reference above, p. 132) in (3):

house Electric Corp.) of (l) for small values of n is obtained from the identity where P and Q denote polynomials, as indicated, wherein are tabulated in Table l TABLE l i n i Anm BMM (E. Madelung--Die Mathematischen Hilfsmittel des Physikers, Berlin, 1936, p. 70) where m denotes the order of the root associated with given n and h; y=(h-1)xn;

The roots, (h-1)xn(m) by graphical solution of (4) for low orders, n, are tabulated in the accompanying Table II.

TABLE II Desired roots of (1) for low orders, n, for the TE mode The desired field configuration .in the concentric spherical cavity determines the .normal mode type required. From the previous table or the onetn p. 206 of the cited "Jahnke- Emde reference the root (h-l)xn(1") corresponding to a specilic normal mode, TEnm Aor THW, can be determined. This permits the evaluation ,of the critical frequency, umn, and geometry, r1, ro, of the concentric spherical resonator according to vthe relation [(hn'lyvnhi 21V(T1'7`o) in gas or vacuum medium.

Consider, for example, the TEoo (or THoo) normal mode in Table Il (or the table on p. 206 of the Jahnke- Emde reference). The corresponding root is Assume r=1 centimeter so that according to Equation at a critical vfrequency of 00:1000 megacycles, r1=16 centimeters. This corresponds to a sphere lapproximately two feet in diameter. Actually, the desired normal mode fields required will be described presently. In any event, these do not necessarily possess the lowest root. Hence, according to expression (5) the sphere diameter, 211, under the same conditions, will be larger by the ratio of the roots (h-1)xn("L)/(h-l)xo().

The lield contiguration and orientation of the desired magnetic component is determined by the size and configuration of the cavity, the frequency of the oscillations and the region and method of excitation with a loop, probe or waveguide.

Holes, friction joints and capacity joints may be placed in the wall of the spherical, or other shell, at proper places to allow for the introduction and removal of the conductive substance, which normally serves initially as the center member of the normally-concentric-spherical resonator produced, as well as for observation of the process of heating the substance and its levitation.

The desired mode of oscillation of the electromagnetic field in the resonator will be modified in relation to the departure of the shape and position of the charge from the ideal. The extent of the eld distortion or contamination of this mode by others in order to satisfy modilied boundary conditions depends upon the particular circumstances. ln any event, appropriate modification of the resonator may be ascertained to eliminate spurious modes caused by such deviations from the ideal by means known in the art.

Referring to the drawing in detail, like parts being designated by like reference characters, and first considering the showing of Figs. 1 to 4 incl., there is illustrated in section through its center, a hollow sphere 11. This sphere is desirably formed as two parts, an upper part 12 and a lower part 13, so that it may conveniently be opened and to allow for the introduction of the conductive mass or object 14 to be melted and/ or heated.

The lower half 13 of the hollow spherical member 11, is desirably held above a table or other supporting device 15, as on standards or columns 16, the upper ends of which carry portions 17 of reduced section. The extreme upper ends of the portions 17 are threaded, as indicated at 18. These portions 17 pass through corresponding apertures in the outstanding flange portions 19 and 21 of the lower and upper segments, respectively, of the hollow spherical member 11. Nuts 22, threaded on the extensions 18, desirably engaging washers 23, serve to hold the sections 12 and 13 together and compress gasket means 24 therebetween, in order to make a gas-tight or vacuum joint.

Coils 25, which may carry a cooling medium such as water, are shown in surrounding contacting relationship with the spherical segments, in order to avoid excessive heating. A means for observation during operation is provided by an eye-piece 26, of hard glass or quartz, and held in place against a boss 27, as by means of aV cap 28 secured to said `boss .by screws 29, .whereby an observer 31 may look through `the hole 32 in thecap and the hole 33 to the boss, to observe the condition of the material 14. Suitable gasket means 34 are provided around -the `edge .of .the eye-piece 26. To reduce electromagnetic field loss and protect the observers eye, the observation hole `diameter must be well beyond cutoff for the highest frequency of tield excited in the resonator.

In .order .to provide for .supplying electromagnetic .energy to the resonator and exhausting and/or `the introduction of a desired atmosphere into the interior of the resonator 11, a hollow desirably cylindrical extension 35 is lprovided and secured to the normally upper por* tion .of the segment 12 at a `corresponding aperture 36, `as by means of Vwelding or ,brazing 37. An annular manifold 38 `encircles ,the hollow ycylindrical portion 35, as

illustrated, and Aconnects `to Athe interior thereof through narrow slits 39, .which allow gas .topass therethrough but ,do Vnot appreciably interfere with .the transmission of power along said cylindrical extension 35, which is adapted Ito function as the outer member of a coaxial cable or line.

The manifold 38 is .connected to ,an exhaust system as by means of a pipe 41, whereas the cylindrical extension `3S is connected to a radio-frequency generator through the joint illustrated in Fig. 3. This joint comprises corresponding heads 42 and 43, respectively formed .on the cylindrical extension 3S and the hollow .cylindrical continuation 44 to the generator. These heads are connected by a section .45, formed as a hollow cylindrical member 4 6 provided with heads 47 and 48, adjustably .connected to the corresponding `heads 42 and 43 `by bolts 49 and l51, which bolts serve to vprovide electrical `continuity between the .members of the l.cylinders 35, 56, 44,

and ,compress packing or gasket means 52 and 53.

In .order 4to seal the space between the Vouter member 35 .of the coaxial line and the inner member 54, which inner 4rnembermay be fabricated from a highly conductive metal such as .copper to which a suitable ceramic (suchas-Coors aI-200) satisfactorily -seals and of tubular form as vthat it may carry a cooling medium such -as water 55, I provide an intermediate hollow cylinder 56 of highly conductive material, such as copper, to which the ceramic is brazed satisfactorily in accord with technique known in the art. Said member 56 is connected to the inner member 54 -by a ceramic seal 57.

To allow for rigidifying the member 56, as well as connecting it to the hollow cylindrical members A35 and44, .without unduly disturbing the continuity of the electrical Connection along the coaxial line, I provide `the connection shown. That is, members 54 and'56 are thinned and fianged as indicated. The cooling medium 55 is kept from direct contact with the portion of `the inner member 54 ,to which the ceramic seal 57 connects by conducting it at this place in an inner tube 58, the ends of which are properly connected to the 'parts of the member above and below said seal, as illustrated in Fig. 3. The ilanges on the ends of the lcopper member 56 are respectively gripped between the members 42 and 47 and the members 43 and 48.

The inner member 54 of the coaxial line is looped back .on itself, as indicated at 65, and connected near the aperture 36 to the spherical portion 12 passing therethrough to the outside coil 25, so as to allow for circulation of the cooling medium 55. The loop is attened, as illustrated in Fig. l, in order to facilitate bending and provide for greater eliiciency of power transfer. The ratio between the ldiameter of the hollow cylindrical conductor 35 and that of the conductor 54 is desirably about 2.7 to l, for lmaximum electrical breakdown strength between the two elements.

In order to allow for insertion and withdrawal of the article or compact mass 14 to be heated, the lower portion of the member 13 lis apertured, as indicated at v66, and ,carries a depending hollow cylindrical flanged collar 67,

secured thereto as by welding or brazing indicated at 68. The collar rests on a block 69 to which it is secured, after the inter-position of gasket or packing means 7l, by means of studs 72 and nuts 73. The block 59 is apertured, as indicated at 74, for exhausting the receiving cup 75. rl`he upper edge of the cup 75 is flanged at '.76 and connected to the block, after the interposition of suitable packing or gasket means 77, as by means of studs 78 and nuts 79. The cup is cooled, as indicated at 31, and pipes 82 and 33 are provided for circulating water or other cooling medium therethrough.

The collar 67 is provided with an inturned or depending iiange 84, of an axial length or height equivalent to about a quarter free space wave length of the electromagnetic power supplied to the apparatus, in order to make it possible to preserve the practical continuity of the resonator surface, as will be explained by the provision of a capacity joint of low impedance. Small apertures 85 are provided in the web which joins the flange 84 to the collar 67, in order to allow for the passage of gas therethrough. A rod 86 of quartz, Vycor or the like, is provided which passes through the aperture left by the ange 3d, through a corresponding aperture in the block 69, and through a corresponding aperture in the bottom wall of the cup 75. The joint where it passes through the bottom wall of the cup 75 is, however, made gastight by suitable packing 87 in a gland 83 held in place by studs 89 and nuts 91.

After the rod 86 has been employed for raising the mass i4 from the dotted line position to the full line position shown in Fig. l, and after the mass has been levitated but before the vacuum is applied, said rod is withdrawn and replaced by a conductive rod 92, preferably formed of high-conductivity metal such as copper, the upper end of which nearly completely fills the aperture in the collar 67 left by the rod 86, in order to preserve the continuity of the spherical segment 13. The lower end of this rod 92 carries a flanged collar 93 connected thereto as by means of a pin 9d, and when properly placed, as illustrated in Fig. l, is by having its ange secured in adjusted position on the studs 89 by nuts 95 and 95. Although no lifting means is illustrated for the rods 36 and 92, it will be understood that conventional means, or such as disclosed in the patent referred to, may be employed.

Figs. 5, 6 and 7 are diagrams illustrating three of the modes of oscillation which the magnetic component of the electromagnetic iield may take, depending on the variables previously referred to. If Fig. 6 is tirst considered and compared with Fig. of the patent previously referred to, the resemblance will be at once apparent. In other words, in both figures, the lines of the magnetic field present convex sides toward the article or material levitated therein, said lines originating at points immediately above and below said article and terminating at points on either side thereof, as indicated by the arrow heads on said lines. Such a mode is produced, in the manner described previously, and by introducing the power at an angle of 45, as indicated by the reference character 35h, designating the outer element of a coaxial cable, the inner element of which is designated by the reference character 541. However, this is not the only useful iield distribution that can be generated in the concentric spherical resonator, for the heating of an object here designated Mb.

Fig. 5 represents another mode in which a suitable magnetic field component i-s obtained, the lines of which are illustrated with arrow heads indicating momentary directions. To produce such a mode, the power is carried in at the top, as by a coaxial line the outer element of which is designated at 35a and the inner element of which is designated 54a. Another lsomewhat rsimilar mode, illustrated in Fig. 7, is produced by varying another parameter as previously discussed and by introducing the power at the top by a coaxial line, the outer element `of which is 35C and the Iinner element 56E-C.

As indicated previously, no resultant electromagnetic levitating force is exerted on the object, ide, Mb or lll-C, in Figs. 5, 6 or 7, in the `symmetrical case shown. r{herefore, the object will settle and in the process distort the fields until the resultant supporting force developed, as a consequence, balances the weight of the object as described in the patent referred to. The modified iield `reduces the stability of the original mode of oscillation and may even destroy it if carried too far. To offset this chance, various modiications can be introduced in the resonator as well as adjustments to the oscillator, depending upon the particular case involved. Non-spherical resonators, as previously mentioned, may also be used to obtain more etfective levitation forces.

Fig. 8 is a view showing an alternative means of introducing power to the resonators, respectively designated lll in Fig. l, llt in Fig. 5, 1lb in Fig. 6, and llc in Fig. 7, comprising a waveguide 97, which is substituted for the coaxial line 35--5-4, 35h-54a, 35h-Elib, 35E-"4, as the case may be. This waveguide although shown hollow cylindrical, may be rectangular, or other form in `sect-ion, as will be understood.

In order to make it possible to maintain a vacuum in the resonator to which the waveguide is connected, the same is closed in gas or vacuum-tight manner by means of a disk 9S, of ceramic such as Coors .Al-209, the edge of which rests on an annular supporting shoulder 99 in the guide, and the periphery of which is at it will be understood that the guide is formed of copper or other metal to which the ceramic disk satisfactorily brazes, after preparation known in the art.

Operation The apparatus illustrated and embodying my invention may be operated as follows:

rEhe upper segment l?. of the resonator is removed from the lower segment i3 by taking olf the nuts ZZ and raising said upper segment. The charge ld is either placed on top of the dielectric rod S6, while raised to the position illustrated in dotted lines, or `on the top of the upper end of said rod while flush with the upper surface at the bottom of the lower segment i3. The resonator is then closed by reapplying the upper segment l2 and tightening the nuts 22 about the threaded portions 13, to provide an air-tight volume enclosed by said resonator.

The dielectric rod 86, if not initially in its up position, may then be elevated to the position shown in dotted lines, where the charge lli takes the position represented in dotted lines. The electromagnetic energy of a specific frequency is then turned on and adjusted to a strength such that the mass 14 is held near the center of the resonator, as the rod S6 is withdrawn. Then the rod d6 is replaced by the metal rod 521, held in the position illustrated in Fig. l so that it completes the practical continuity of the lower spherical segment The observer 3l looking through the eye-piece 2e can determine the position and state of the charge lid. lt will be understood that although it may be initially raised to the midpoint of the resonator, yet upon removal of the `supporting rod 36, it will settle down to a position indicated at 14 in full lines (assuming a bulging shape as there illustrated when and if melted) at which the resul*- ant electromagnetic forces balance the weight of the charge and prevent lateral drift.

lf it is desired to effect melting and/or heating in an inert or reducing atmosphere or vacuum, the exhaust pump is then turned on to withdraw the air from the resonator through the pipe 4l. When a sutlicient degree of vacuum has been obtained, or inert gas substituted for the air withdrawn through the slits 39, the power delivered to the resonator is correspondingly adjusted until the desired melting and/ or heating effect is obtained.

lf melting is desired, then the rod 92 after melting takes place, is withdrawn from the position shown in Fig. l to that `shown in Fig. 4, where it opens the bottom of the resonator ll and eliects a corresponding closure ofthe water cooled cup 75. While this melting i-s going on, the water or other cooling medium is circulated through the cooling coils Z to prevent overheating of the resonator. When the desired melting has been obtained, as can oe determined by observation through eye-piece 26, the power supplied to the resonator is adjusted downward until the molten metal Hows from the mass 14, as illustrated by solid lines, into the cup 75, as shown lmost clearly in Fig. 4.

The draining process may, but not necessarily, impose new boundary conditions in a particular type or" resonator and so may require excitation of an appropriate mode in order to prevent collapse of the original mode and consequent dropping of the whole molten charge.

It may he feasible to alter the thermal environment sufficiently to solidify the molten charge and drop it whole to the position designated at 14. Due to the sigmoidal relation of levitation to frequency and reverse sigmoidal relation of heating to frequency, a decrease of frequency may rapidly decrease heating, while not substantially `affecting the levitation force (i. of Appl, Phys., May and December 1952) depending upon the particular circumstances. Orientation of the field by changing the method of excitation may also allow draining without collapsing the original mode. A reduction in frequency and consequent change of mode may be realized without dropping the molten charge.

During the time the cup 7S is receiving moiten metal, water or other cooling medium should be circulated in the pipe 82 and out of the pipe 83, in order to prevent overheating of said cup and contamination of the charge. When all of the molten material has been drawn into the cup 75 and allowed to cool therein, the power may be turned oii, the vacuum in the system relieved, and the nuts 79 removed to allow withdrawing the cup and its contents from the resonator for the purpose desired.

The size of the generator for operating such a resonator will depend on a number of factors, such as relative size of the resonator, which may vary in diameter from one to several feet, and will also depend on the weight and electrical properties of the charge, and the temperature it is to be heated. The thickness of the resonator wall will depend on its size and usage to which it is to be subjected, and will be understood and calculable by those skilled in the art. The patent previously referred to may be consulted for the weights and kinds of material which may be raised and melted, for given amounts of power introduced therein, with the understanding that the arrangement of the present application is more ethcient and, therefore, more eiiicient levitation and heat can be introduced into the work with a given amount of power available, than with the apparatus of the patent referred to.

It will also be understood that although a conductive sphere of the material worked on has been considered for simplicity, other forms of conductive material may be used with etectiveness. Although a ceramic, such as Coors AI-200, has been suggested for the discs 57 and 98, it will be understood that other materials, including glass, having similar electrical and physical properties, or which will function to provide satisfactory bond, may

10 be substituted. It will also be understood that magnetic solid material, as well as non-magnetic material, may be heated and melted as desired.

Although preferred embodiments of my invention have been disclosed, it will be understood that modifications may be made within the spirit and scope of the invention.

I claim:

l. Apparatus for levitating and heating electricallyconductive material comprising a hollow conductive body separable into two sections, a charge of electricallyconductive material within said body, means for hermetically sealing the body, and means for supplying high frequency power to said body to form a cavity resonator and generate an electromagnetic iield of preselected configuration to levitate and heat the material while sealed from the atmosphere, one of the said body sections having an aperture therein and carrying a non-conductive rod replaceable by a conductive rod and reciprocable in said aperture to permit positioning the charge within the supporting iniiuence of the electromagnetic field without disturbing the iield coniiguration and after levitation has been eifected to plug said aperture with conductive material and preserve the continuity of the resonator.

2. Apparatus for levitating, heating and melting electrically-conductive material comprising a hollow conductive body having an axially disposed aperture in the bottom portion thereof, a charge of electrically-conductive material within said body, retractable means recip` rocable in said aperture for orienting and temporarily supporting said material in a xed predetermined spaced position within and along the axis of said body, means for hermetically sealing said body, means for supplying high frequency power of variable frequency to said body to form a cavity resonator and generate an electromagnetic iield of preselected coniiguration to levitate the material after said retractable supporting means have been activated and to heat the material while sealed from the atmosphere until it melts7 a cup disposed below and in coaxial alignment with said charge and the aperture through the bottom portion of said body to receive the molten material, and means for cooling the cup, said cup having an axially disposed aperture through its bottom for reception of said retractable orienting and temporary supporting means. l

3. Apparatus for levitating, heating and melting electrically-conductive material as set forth in claim 2 wherein the said power-supplying means carries means for eX- hausting the interior of the cavity resonator and said body carries cooling means along its exterior surface to prevent excessive heating thereof during operation.

References Cited in the le of this patent UNITED STATES PATENTS 2,491,418 Schlesman Dec. 13, 1949 2,497,670 Hanson et al Feb. 14, 2,548,598 Feiker Apr. 10, 1951 2,585,970 Shaw Feb. 19, 1952 2,620,172 Jenett et al. Dec. 2, 1952 2,664,496 Brace Dec. 29, 1953 2,686,864 Wroughton et a1. Aug. 17, 1954 

